A display device employing a touch panel as an input device comprises: a display panel for displaying an image, and the touch panel which is placed over the display panel. An electrostatic capacitance method, in which contact of a finger or the like with an operating surface of the touch panel is detected as a change in electrostatic capacity, is widely used as a method for detecting a contact position of a finger or the like on the touch panel. In a touch panel employing an electrostatic capacitance method, a conductive film of the touch panel comprises: a plurality of first electrodes extending along a first direction, a plurality of second electrodes extending along a second direction orthogonal to the first direction, and a transparent dielectric layer interposed between the first electrodes and the second electrodes. The contact position of a finger or the like on the operating surface is then detected on the basis of a change in electrostatic capacity between one first electrode and each of the plurality of second electrodes being detected for each first electrode.
In one example of such a conductive film, each of the plurality of first electrodes comprises a plurality of first electrode wires extending along the first direction, and each of the plurality of second electrodes comprises a plurality of second electrode wires extending along the second direction. Thin wires comprising a metal such as silver or copper are used as the electrode wires. Using a metal as the material for the electrode wires allows a rapid response and a high resolution to be obtained when the position of contact is detected, while also enabling an increase in the size of the touch panel and a reduction in production costs.
In a form in which the electrode wires comprise a metal which absorbs or reflects visible light, the plurality of first electrode wires and the plurality of second electrode wires form a grid-shaped pattern in which the electrode wires are orthogonal to one another, when viewed from a direction facing the operating surface. Meanwhile, in the display panel to which the touch panel is laminated, a grid-shaped pattern is also formed by a black matrix defining a plurality of pixels along the first direction and the second direction.
In the abovementioned configuration, the interval between adjacent first electrode wires is generally different from the interval in the second direction between adjacent pixels, and the interval between adjacent second electrode wires is different from the interval in the first direction between adjacent pixels. Furthermore, when viewed from a direction facing the operating surface, a grid-shaped periodic structure formed by the first electrode wires and the second electrode wires lies over a grid-shaped periodic structure defining the pixels, as a result of which an offset between the two periodic structures may give rise to moiré. Observing moiré causes a deterioration in the quality of images observed on the display device.
One countermeasure that has been proposed to suppress such moiré is to reduce the periodicity of the periodic structure of the electrode wires. If the periodicity of the pattern formed by the plurality of electrode wires is low, the electrode wire pattern is less likely to be observed as a periodic structure, so an offset between the pixel pattern, which is the pattern defining the pixels, and the electrode wire pattern is less likely to be observed as an offset between two periodic structures. Observation of moiré is consequently suppressed.
In the touch panel described in WO 2014/115831, for example, the first electrode wires and the second electrode wires each have a polygonal line shape in which ridge portions and valley portions are repeated alternately, and a pattern formed by these electrode wires has a repeating structure comprising polygons other than rectangles. The periodicity of such an electrode wire pattern is therefore lower than the periodicity of a grid-shaped electrode wire pattern in which rectangles are arranged.